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Spitzer spies potential planet-harbouring binaries

Paging Mr Skywalker

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Astronomers using the Spitzer space telescope have discovered that, contrary to expectations, twin-star systems are actually more likely to have indictors of planetary systems than single stars are.

The discovery has got everyone very excited because it means Luke Skywalker's home world, with its double sun, is not a total* fantasy.

The researchers found that twin-star systems, complete with dusty disks of asteroid and comets, are at least as common as single star systems boasting the same kind of debris, if not slightly more so.

David Trilling of the University of Arizona, Tucson, lead author of a new paper about the research to be published in the 1 April issue of the Astrophysical Journal, said: "There appears to be no bias against having planetary system formation in binary systems. There could be countless planets out there with two or more suns."

NASA goes even further, suggesting that among the many millions of worlds out there, some must have the same kind of configuration as Tatooine, one sun slowly following another over the horizon.

Astronomers have known for a while that planets can form in very widely spaced binaries: roughly 1,000 astronomical units (AU) apart. But this research concentrates on twin systems with a separation of between 0-500 AU.

Having located its relatively tightly bound binary pairs, the team then used Spitzer's infrared cameras to seek out debris disks - the swirls of asteroids and dust that are indicative of planet forming.

NASA says of the 69 systems they studied, 40 per cent had disks, rising to 60 per cent if the group was restricted to the tightest systems in the sample. Binary systems spaced between 3-50AU had fewer disks, suggesting that for planets to form in a binary system, the stars must either be quite close together, or relatively far apart.

"We were very surprised to find that the tight group had more disks," said Trilling. "This could mean that planet formation favours tight binaries over single stars, but it could also mean tight binaries are just dustier. Future observations should provide a better answer."

Spitzer also found disks that orbit the pair of stars, rather than just one. And it is in these systems that Luke Skywalker would feel most at home. ®